1. Field of the Invention
The present invention relates to a sealed type thermometer resistance element which is employed for measuring precision temperature, and more particularly to a thermometer resistance element which comprises a coil-shaped resistor for measuring temperature which is located in a slender ceramic tube together with a filler which consists of finely divided spherical particles and which is adapted to fix the resistor. Furthermore, the present invention relates to a thermometer resistance element assembly which comprises a thermometer resistance element and a heat transmitting member on which the thermometer resistance element can easily be mounted and placed into a protective tube.
2. Brief Description of the Prior Art
It is necessary not only that the thermometer resistance element of this type should, of course, satisfy a variety of electrical efficiencies stipulated in the Regulations in a range for measuring temperature, but also that the thermometer resistance element be as small and as light as possible, and that both physical and mechanical properties, such as temperature-response characteristic, shock-proof, etc. be excellent.
There is known a thermometer resistance element which comprises a coil-shaped resistor, such as a platinum wire, etc., placed in a bore of a ceramic insulating tube, together with fillers.
However, conventional fillers are made of crushed electrofused alumina or quartz glass. An enlarged view of the shape of these fillers shows an amorphous state of crushed fragments having sharp wedge portions, as in cracked rocks. Moreover, the size of each particle is uneven.
It is next to impossible to uniformly fill up with such uneven particles the bore of the insulating tube having a diameter of 0.8 mm in which a resistor having a coil diameter of 0.4 mm is housed, without the help of a special apparatus. In addition to such a difficulty, unevenness in packing density is liable to occur in the longitudinal direction of the bore, and it is substantially impossible to uniformly fill up the inner side of a coil having a small coil diameter.
Further, it is very likely that filler particles do not get between the coils (or turns) of a coil-shaped resistance wire.
Fillers are expected not only to merely affix a coil-shaped resistor into the insulating tube but also to stably hold the resistor without any deviation in the tube bore, and to maintain a linear state of the coil-shaped wire upon its insertion along the tube bore.
Further, fillers should maintain a uniform pitch of the coils and should not cause any electrical short circuit of the coils when expansion and contraction of the coil occur due to temperature change over a wide range.
For these reasons, it is necessary that filler particles fill a tube with a uniform density, including the spaces (about 50 to 80 .mu.m) between the coils.
Accordingly, it is desired that fillers have a fluid-like capability but should not scatter at the time when they are packed in the tube, and also they should be highly and electrically insulative and be in the form of a single solid.